Various kinds of image forming materials having various structures and compositions and various image forming methods using these materials have been known. Typically, these include silver halide light-sensitive systems (black and white photography, color photography, dry silver light-sensitive thermography, instant photography, etc.), photopolymer systems (printing plates, photoresist, etc.), diazonium coloring systems, free radial photographic systems, etc. Each system has established each independent application field by the various features thereof based on the specific structure and composition of the image forming materials being used.
Another image forming system comprises an image forming system using a cation dye/boron compound anion salt. For example, a light-sensitive pressure-sensitive type image forming system has been disclosed wherein a cation dye/boron compound anion salt is used as a photopolymerization initiator and the salt is encapsulated in microcapsules together with a polymeric monomer and a basic dye precursor, in JP-A-No. 62-143044 and JP-A-No. 62-150242 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
In the system, images are formed by utilizing the characteristic of the microcapsules that (1) they are hardened (become non-collapsing) by the action of light or (2) undergo a coloring reaction (the coloring reaction occurring by the contact of the basic dye precursor and an acid developer) by collapse upon application of pressure to the microcapsules at unexposed portions.
Also, an image forming system using a cation dye/boron compound anion salt belonging to a dye-bleach-out type is disclosed, for example, in U.S. Pat. Nos. 4,307,182, 4,343,891, 4,450,227, and 4,447,521. The system is a so-called positive type image forming system wherein a cation dye/boron compound anion salt is dissolved in an organic solvent together with a polymer binder and coated on a support, and a bleaching action occurring upon light exposure corresponding to the absorption wavelength of the cation dye is utilized for the image formation.
However, in the aforesaid dye-bleach-out type image forming system, since the image forming material being used in the system is susceptible to light, when the image forming material is exposed to ordinary room light, sun light, or white light even after forming images by light exposure, dye bleaching occurs, and hence handling of such an image forming material is not easy.
For stably preserving the images after formation, the occurrence of dye bleaching at the portions which were not exposed at the image exposure must avoid. For example, it is known to apply a compound capable of cleaving one or more carbon-boron bonds (i.e., fixing agent) onto a material having images formed by impregnation, spraying, coating, vapor exposure, etc., as disclosed, e.g., in U.S. Pat. No. 4,343,891 described above and the images can be stably preserved. This is advantageous for the preservation or fixing of images, but since the aforesaid process is a wet process, the operation is complicated and hence such a process is unpreferably.
On the other hand, for preparing the aforesaid dye-bleach-out bleaching type image forming material composed of a cationic dye/boron compound anion salt, the aforesaid components are usually uniformly dissolved in an organic solvent, coated on a support such as a paper or a plastic film, and the solvent is distilled off by drying. An impregnation or flow stretching may be employed in place of coating. Thus, with the use of such a volatile organic solvent, means for preventing explosions are required for the production equipment, and the aforesaid process is disadvantageous from the viewpoints of safety and cost.
Furthermore, in the case of preparing multicolor image forming materials, multilayer coating of at least three layers (e.g., A color layer/interlayer/B color layer) is required in addition to a means for preventing color mixing, etc., which require specific equipment. If it is possible to not use such multilayer coating equipment, it is, as a matter of course, preferred.